I have hunted many years with real light colored yellow dogs and have lost more to gators than hogs. I have seen a lot of dark colored dogs, belonging to people that hunted with me, killed or injured by hogs. Maybe the hogs just pick out the odd dog in the bunch or the ones that don't have the sense or athleticism to get out of the way.
I think you are right on, and probably a mixture of all of the factors you mentioned.
I know when I was up hunting bear the last couple of years that my bear hunting partners fully believes that the dog with the odd color out will get targeted.
